Circuit, system and method for selectively turning off internal clock drivers

ABSTRACT

The present invention includes a circuit, system and method for selectively turning off internal clock drivers to reduce operating current. The present invention may be used to reduce power consumption by reducing operating current in a memory device. Operating current may be reduced by turning off internal clock drivers that deliver a clock signal during selected periods of time. According to an embodiment of clock control circuitry of the present invention, an internal clock is disabled if a no operation command is detected during periods of time when no read or write burst operation is taking place. Methods, memory devices and computer systems including the clock control circuitry and its functionality are also disclosed.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/652,897, filed Jan. 6, 2010, which is a continuation of U.S.application Ser. No. 11/449,499, filed Jun. 7, 2006, now U.S. Pat. No.7,669,068, issued Feb. 23, 2010, which is a continuation of U.S.application Ser. No. 10/179,882, filed Jun. 25, 2002, now U.S. Pat. No.7,089,438, issued Aug. 8, 2006. The entire teachings of the aboveapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

There are many reasons why reducing operating current in digitalelectronics, especially computer systems, is desirable. Portablecomputer systems, for example, rely on battery power when not pluggedinto a recharger. By reducing power consumption, batteries will lastlonger between recharging and the user has more time to performcomputing tasks untethered by a power cord. Even desktop computers canbenefit from reduced operating current by the cumulative effects ofenergy consumption, thereby reducing energy needs and related costs toconsumers.

At the integrated circuit level, reducing operating current generallyreduces power consumption. More importantly, reducing operating currentreduces the need for heat dissipation. With an ever-increasing number oftransistors on a single integrated circuit (IC) chip, heat dissipationbecomes a serious concern because over-heated electronic devices aremore likely to fail from thermal breakdown or simply by burning up. Thecost of electronic systems increases when the use of heat sinks, fansand other means of cooling is necessary to cool the ICs within.

The prior art has taken a number of approaches to reducing powerconsumption in digital electronic systems. One conventional approach,common in laptop personal computers, involves shutting down certainfunctions, e.g., hard drives and displays, after a period of inactivity.This approach typically requires the use of software or hardware timers.Another approach, know as “clock throttling,” reduces power consumptionby reducing the speed of the clock driving the digital circuitry. Sincepower consumption is directly related to clock speed, any reduction inclock speed will reduce power consumption.

These prior art approaches suffer from a variety of shortcomings. Forexample, if functional aspects of a system are temporarily turned off toreduce power consumption, these same functional aspects are notimmediately available to the system user. For example, a hard drive thathas been shut down may need to spin up for a few seconds in order to beaccessed. Such delays can be annoying and waste the user's time.Additionally, such power-reducing schemes implemented in software willconsume computational resources. Similarly, where timers are implementedin hardware, additional computer hardware is required, adding to systemcost, and may also consume valuable IC real estate. The clock throttlingapproach directly affects system performance. If a system clock isreduced in half, a given task may take twice as long to perform.

Another conventional approach to reducing power consumption in ICs isdisclosed in U.S. Pat. No. Re. 36,839 to Simmons et al. The Simmons etal., patent discloses clock control circuitry coupled to functionalblocks. The clock control circuitry activates and deactivates thefunctional blocks in response to the flow of data within the IC bymodulating clock signals distributed to the functional blocks. However,the functional blocks must provide control signals to the clock controlcircuitry requesting that it and/or its neighbor be activated ordeactivated. Additionally, Simmons et al., does not appear to disclosemonitoring external (off-chip) signals suitable for selectively turningoff internal clock drivers for reducing power consumption in a memorydevice.

U.S. Pat. No. 5,615,376 to Ranganathan discloses clock management forpower reduction in a video display subsystem. According to theRanganathan patent, a video subsystem reduces power consumption byperiodically disabling the video controller clocks used for transferringpixel data to a screen. The video clocks are pulsed only when pixel datais being transferred to the screen, during the time that a horizontalline of pixels is being scanned on the screen. The video clocks are notpulsed during the horizontal and vertical blanking periods, when theelectron beam in a cathode-ray-tube is being retraced. The video clocksare also not pulsed during a recovery period for a flat-panel display.However, the Ranganathan patent appears to be tailored to videosubsystems and does not appear to disclose monitoring external(off-chip) signals suitable for selectively turning off internal clockdrivers for reducing power consumption in a memory device.

Yet another conventional method of reducing power consumption in ICs isdisclosed in U.S. Pat. No. 5,918,058 to Budd. Budd discloses routing ofclock signals in a data processing circuit with a power-saving mode ofoperation. The data processing circuit according to Budd comprises aclock generator for generating a clock signal and a plurality of clockedcircuit elements. A main bus is arranged to provide the clock signal tothe plurality of clocked circuit elements in a first mode of operationand a power-saving bus separate from the main bus arranged to providethe clock signal to a subset of the plurality of the clocked circuitelements in a power-saving mode. The obvious shortcoming with the Buddapproach is the necessity for two clock busses. Additionally, Budd doesnot appear to disclose monitoring external (off-chip) signals suitablefor selectively turning off internal clock drivers for reducing powerconsumption in a memory device.

Thus, there exists a need in the art for a circuit, system and methodfor selectively turning off internal clock drivers by monitoringexternal signals suitable for reducing operating current in memorydevices.

SUMMARY OF THE INVENTION

The present invention includes a circuit, system and method forselectively turning off internal clock drivers to reduce operatingcurrent. Advantages of the circuit, system and method of the presentinvention include reducing operating current in an IC during idle time.By reducing operating current, power consumption is also reduced,thereby increasing battery life for portable systems relying on batterypower. Additionally, by reducing power consumption, cooling requirementsare also reduced for ICs including the clock control circuitry of thepresent invention. The invention is particularly suited for detectingidle time in a memory device such as a dynamic random access memory(DRAM) and turning off internal clocks driving global cells within thememory device or the whole die depending on whether the die is actuallyperforming an active function.

The embodiments of the present invention will be readily understood byreading the following detailed description in conjunction with theaccompanying figures of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of clock control circuitry in accordancewith the present invention.

FIGS. 2A-B are schematic diagrams of another embodiment of clock controlcircuitry according to the present invention.

FIGS. 3A-B are schematic diagrams of a clock buffer including clockcontrol circuitry as shown in FIGS. 2A-B according to the presentinvention.

FIG. 4 is a block diagram of a memory device that may include clockcontrol circuitry or a clock buffer according to the present invention.

FIG. 5 is a flow chart of a method of reducing power consumption in amemory device in accordance with the present invention.

FIG. 6 is a plan view of a semiconductor substrate including at leastone IC die having clock control circuitry or a clock buffer of thepresent invention.

FIG. 7 is a block diagram of a computer system according to the presentinvention.

The foregoing will be apparent from the following more particulardescription of example embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingembodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates generally to integrated circuits. In particular,the present invention relates to a circuit, system and method forselectively turning off internal clock drivers to reduce operatingcurrent.

A description of example embodiments of the invention follows.

The present invention includes a circuit, system and method forselectively turning off internal clock drivers to reduce operatingcurrent. The present invention may be used to reduce power consumptionin a memory device. The reduction in power consumption may be obtainedby reducing operating current in the memory device. Operating currentmay be reduced by turning off internal clock drivers that deliver aclock signal during selected periods of time. When internal circuitrydoes not require a clock signal, there is no need to distribute a clocksignal that requires constant switching of transistors.

FIG. 1 is a schematic diagram of clock control circuitry 100 inaccordance with the present invention. Clock control circuitry 100receives a system clock (CLKIN) as an input signal and selectivelyoutputs an internal clock (CLKOUT) for use by other synchronouscircuits. Clock control circuitry 100 may include command detectioncircuitry 102 and clock gating circuitry 104 coupled to said commanddetection circuitry 102. Clock control circuitry 100 may also includedelay circuitry 106 for delaying a system clock to compensate for delaysin the command detection circuitry 102.

Command detection circuitry 102 may include any circuitry for monitoringcommand signal inputs to determine occurrence of an active command,e.g., a read or write command, or, alternatively, if the memory deviceis to remain idle, e.g., a no operation (NOP) command. As illustrated inFIG. 1, command detection circuitry 102 may include a 3-input NAND gate108 for sensing an NOP command. During an NOP command, no action oroperation takes place in response to command signal inputs. It isdesirable to turn off an unneeded internal clock during an NOP command.In a memory device, an NOP command may be sensed by the signalsrow-address strobe (RAS_), column-address strobe (CAS_) and write enable(WE_) as shown in FIG. 1. The “_” symbol appended to RAS_, CAS_andWE_indicates that the signals RAS_, CAS_and WE_are active low. Ofcourse, one of ordinary skill in the art will recognize that selectingRAS, CAS and WE to be active high or active low is a simple matter oflogic design. Thus, the use of active low RAS_, CAS_and WE_is merelyexemplary. Three-input NAND gate 108 will output signal NOP_(active low)indicating an NOP command if RAS_, CAS_and WE_are all high.

Command detection circuitry 102 may also include burst detectioncircuitry 110. Burst detection circuitry 110 detects whether or not aread or write (read/write) burst operation is taking place. While it isdesirable to turn off an internal clock during idle time, it isimportant to distribute an internal clock during read/write burstoperations. If a read/write burst operation is taking place, burstdetection circuitry 110 provides a signal to clock gating circuitry 104allowing distribution of a system clock as an internal clock, regardlessof the output of 3-input NAND gate 108 and the presence of an NOPcommand. As shown in FIG. 1, input signals WEN and ENOUT are input to a2-input NOR gate 112, the output of which feeds an inverter 114 drivingsignal NOBURST_. Of course, there are other combinations of logic gateslogically equivalent to the 2-input NOR gate 112 and inverter 114, e.g.,a 2-input OR gate in series with a buffer. Such equivalent combinationsof logic gates are within the scope of the present invention and alsowithin the knowledge of one of ordinary skill in the art and, thus, willnot be further elaborated.

Command detection circuitry 102 may further include bypass circuitry 116for selectively bypassing the power conservation feature of the clockcontrol circuitry 100. Bypass circuitry 116 may be a switch (asillustrated) or may be a nonvolatile programmable element such as a fuseor antifuse, or may be a volatile switching element such as atransistor, latch or register, or any other suitable means for settingthe value of signal NOBURST_. Command detection circuitry 102 mayfurther include a 2-input NOR gate 118 for receiving signals NOP_andNOBURST_and outputting signal GATECLK_. If signal GATECLK_is held high,output signal CLKOUT will always be held low regardless of levels oredges on input signal CLKIN. Alternatively, if GATECLK_is low,indicating a non-NOP command or a burst operation, pulses on inputsignal CLKIN will propagate to output signal CLKOUT. Command detectioncircuitry 102 may further include an input inverter 120 and outputinverters 122 and 124 for buffering the input signal CLKIN and outputsignal CLKOUT, respectively. Output inverters 122 and 124 may be sizedto drive an appropriate fan out as known to one of ordinary skill in theart.

FIG. 2 is a schematic diagram of clock control circuitry 200 accordingto the present invention. Clock control circuitry 200 may includecommand detection circuitry 202, burst detection circuitry 204 and clockgating circuitry 206 coupled to the command detection circuitry 202 andthe burst detection circuitry 204. The output signal CLKOUT_EN_may beused by other circuitry (not shown in FIG. 2, but see FIG. 3 and relateddiscussion below) to disable distribution of a system clock (not shown)to other internal circuitry during idle time, thereby reducing powerconsumption.

Input signals to clock control circuitry 200 may include command signalssuch as FCMD_<0:3>, which may be decoded to determine when an activecommand or NOP command is present; a preclock signal PRE_CK, which maybe used to qualify commands in a register 208 (see below); input clocksignal CLKPDQ_, which is indicative of the system clock signal (notshown) that is to be distributed internally or not; register burstcontrol signals such as RB<0:3>, which may be decoded along with anenable out ENOUT signal to determine whether or not a read/write burstoperation is being executed. An optional power up PWRUP signal may alsobe input to clock control circuitry 200 for forcing the output signalCLKOUT_EN_to an on state until a valid power up condition is detected.Additionally, signals TEST and PFTM may be used as spare control signalsfor test modes. The output signal to clock control circuitry 200 mayinclude CLKOUT_EN_as further described below.

Clock control circuitry 200 may further include a register 208 coupledto the command detection circuitry 202 for assuring valid commands andavoiding potential race conditions. Register 208 may avoid raceconditions by ensuring CLKOUT_EN_is low for a minimum of two preclockpulses for every active command. The operation of register 208 will beapparent to one of ordinary skill in the art and, thus, will not befurther elaborated herein. Clock control circuitry 200 may furtherinclude delay circuitry 216 to adjust the timing of input clock signalCLKPDQ_relative to delays caused by the burst detection circuitry 204.

Burst detection circuitry 204 may include optional bypass circuitry 210to disable the power savings feature of the clock control circuitry 200.Optional bypass circuitry 210 may be a switch (as illustrated) or may bea nonvolatile programmable element such as a fuse or antifuse, or may bea volatile switching element such as a transistor, latch or register, orany other suitable means for disabling the power savings feature of theclock control circuitry 200 of the present invention. Burst detectioncircuitry 204 may further include spare control circuitry 212 for testmodes as known to one of ordinary skill in the art.

Command detection circuitry 202 may be used to decode command signals todetermine whether an NOP command has been issued or not. Commanddetection circuitry 202 may be a 4-input NAND gate 214 for detectingsignals on FCMD_<0:3> corresponding to RAS, CAS and WE as describedabove and chip select (CS). If all four bits or signals of FCMD_<0:3>are high, then an NOP command has been detected. Otherwise, some otheractive command is present. Other logically equivalent combinations ofgates may be substituted for the command detection circuitry 202illustrated in FIG. 2 and are considered to be within the spirit andscope of the present invention.

Clock control circuitry 200 may be used on any applicable dynamic randomaccess memory (DRAM) memory device, for example and not by way oflimitation, a dynamic random access memory (DRAM), double data rateSDRAM (DDR SDRAM), RAMBUS® DRAM (RDRAM®), extended data-out DRAM (EDODRAM) and fast-page-mode DRAM (FPM DRAM).

FIG. 3 is a schematic diagram of a clock buffer 300 including clockcontrol circuitry 200 in accordance with the present invention forselectively driving one or more internal clocks derived from a systemclock. Clock buffer 300 may also include clock receiving circuitry 304for receiving an external system clock labeled “clk” in FIG. 3. Clockcontrol circuitry 200 provides CLKOUT_EN_as an active low signal todisable an internal clock when not needed. Clock buffer 300 may furtherinclude other circuitry for receiving CLKOUT_EN_and disablingdistribution of the external system clock “clk” if CLKOUT_EN_is low. Forexample, clock buffer 300 may include clock pulse circuitry 302 (labeled“clk_pulse,” two of which are shown in FIG. 3) for receivingCLKOUT_EN_and selectively driving or disabling the system clock receivedon the input signal labeled CLKIN as it is distributed to the outputsignal labeled CLKOUT to other circuitry (not shown). Clock buffer 300selectively delivers internal clock signal CLKPDQ in accordance with thestate of CLKOUT_EN_. For example, if CLKOUT_EN_is low, then internalclock signal CLKPDQ is output from clock buffer 300, whereas ifCLKOUT_EN_is high, internal clock signal CLKPDQ is disabled, thusreducing power consumption. Thus, CLKOUT_EN_is used to enable or disableCLKP_.

Clock control circuitry 100 and 200 and clock buffer 300 of the presentinvention may be used in any higher order digital logic device or ICthat may be suitable for reducing power consumption by turning off aninternal clock as described herein. For example, FIG. 4 is a blockdiagram of a memory device 400 that may include clock control circuitry100 and 200 or clock buffer 300 according to the present invention.Memory device 400 may be, for example and not by way of limitation, adynamic random access memory (DRAM), double data rate SDRAM (DDR SDRAM),RAMBUS® DRAM (RDRAM®), extended data-out DRAM (EDO DRAM) orfast-page-mode DRAM (FPM DRAM).

FIG. 5 is a flow chart of a method 500 of reducing power consumption ina memory device in accordance with the present invention. Method 500 mayinclude sensing 502 a no operation (NOP) command, determining 504whether or not a read/write burst operation is active and selectivelyturning off 506 distribution of a system clock within a memory device ifthe NOP command is active and the read/write burst operation is notactive. Sensing 502 an NOP command may include monitoring RAS, CAS, WEand CS signals. Determining 504 whether or not a read/write burstoperation is active may include monitoring register burst control andenable out signals.

Referring to FIG. 6, a plan view of a semiconductor substrate 600 isshown including at least one IC die 602 (only one of which is shown forclarity). Each IC die 602 may be a memory device 400 including clockcontrol circuitry 100, 200 and/or clock buffer 300 of the presentinvention. Alternatively, integrated circuit die 602 may be any otherintegrated circuit that may have an internal clock that may be turnedoff during idle time in accordance with the present invention.Semiconductor substrate 600 may be a silicon wafer or other large-scalesubstrate comprising a layer of semiconductor material.

The semiconductor technology employed is not a limiting factor in theapplication of the circuits and systems of the present invention. Whilesilicon is the preferred bulk semiconductor material for commercialelectronic devices, gallium arsenide and indium phosphide substrates mayalso be employed. Of course, it will be understood that the devices ofthe present invention may be fabricated on other semiconductorsubstrates as well, including, for example, silicon-on-glass (SOG)substrates, silicon-on-insulator (SOI) substrates, andsilicon-on-sapphire (SOS) substrates.

FIG. 7 is a block diagram of a computer system 700 in accordance withthe present invention. System 700 may include an input device 702,output device 704 and processor 706 in communication with the inputdevice 702 and output device 704. System 700 may further include amemory device 400 including clock control circuitry 100, 200 and/orclock buffer 300 of the present invention.

Although this invention has been described with reference to particularembodiments, the invention is not limited to these describedembodiments. The invention is limited only by the appended claims, whichinclude within their scope all equivalent devices or methods thatoperate according to the principles of the invention as describedherein.

The teachings of all patents, published applications and referencescited herein are incorporated by reference in their entirety.

While this invention has been particularly shown and described withreferences to example embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A memory device, comprising: a memory array; andclock control circuitry in communication with said memory array and forreceiving a system clock, said clock control circuitry comprising:command detection circuitry configured to generate a gating signalindicating idle time in a memory device based on command signal input tothe memory device; and clock gating circuitry coupled to said commanddetection circuitry for receiving said system clock and for selectivelygating said system clock in response to said gating signal.